Kinematics and velocity ellipsoid of M giants

BRANHAM, RICHARD L. JR.

REVISTA MEXICANA DE ASTRONOMíA Y ASTROFíSICA

Año: 2008 vol. 44 p. 29 - 43

0185-1101

To study the kinematics of M giant stars (luminosity class III) use is made of 1,532 stars with proper motions taken from the \textit{Hipparcos} catalog, of which 480 have radial velocities taken from other sources. Stars farther off than 700 pc were excluded because they induce a noticeable tilt in the distribution of the stars. Various solutions were performed, and the one calculated by the robust L$_{1}$ norm was taken as the best. Semi-definite programming solves for the kinematical parameters such as the Oort constants and simultaneously for the coefficients of the velocity ellipsoid. The results obtained are reasonable: solar velocity of 24.20$\pm 0.70$ km s$^{-1};$ Oort's constant's, in units of km s$^{-1}$ kpc$ ^{-1},$ $A=16.86\pm 2.78$ and $B=-6.34\pm 2.56,$ implying a rotational velocity of 197.27$\pm 26.80$ km s$^{-1}$ if we take the distance to the Galactic center as 8.5$\pm 1.1$ kpc; velocity dispersions, in units of km s$ ^{-1}$, of: $\sigma _{x}=57.40\pm 1.67,$ $\sigma _{y}=45.86\pm 1.63,$ $ \sigma _{z}=33.84\pm 1.02$ with a vertex deviation of -9.$^{\circ }22\pm 4.^{\circ }97.$